Trimmer condenser



March 5, 1945. G M EHLERS ET AL I '2,37o,722

TRIMMER CONDENSER Filed Nov. 2'7, 1940 INVENTOR GEORGE AZ [HIE/P5 Z2 2/ Jail/V 5. comm 44.

GEO/76E Kan/mm.

7. BY w. m m

AT TOR NEY.

Patented Mar. 6, 1945 TRIMMER. CONDENSER George M. Ehlers, John S. Coldwell, and George Kodama, Milwaukee, Wis., assignors to Globe- Union, Inc., Milwaukee, Wis., a corporation of Delaware Application November 27, 1940, Serial No. 367,430

Claims.

This invention relates to an improvement in trimmer or padding condensers usually employed to tune in a final and precise fashion resonant circuits of radio receivers to fixed selected frequencies.

Among the objects of the present invention areto simplify and compact the construction of such a condenser, to enhance its efiiciency, prolong its life, and to facilitate its economical production on a commercial scale.

Another and important object of the invention is to provide a condenser of this character, which,

while possessing the advantages mentioned, renders available a wide range of capacities and makes feasible and practical a minute variation in, or a very fine adjustment of, the capacities which may be selected over the entire range.

A further object of the invention is to facilitate the changing or variation of the capacities available.

Other objects and advantages reside in certain novel features of the construction, arrangement, and combination of parts, which will be hereinafter more fully described and particularly pointed out in the appended claims, reference being had to the accompanyingdrawing forming a part of this specification, and in which:

Figure 1 is a view in top plan showing a trimmer condenser embodying the present invention.

Figure 2 is a view in longitudinal vertical cross section taken on line 2-2 of Figure 1 and looking in the direction of the arrows.

Figure 3 is a view in bottom plan of the condenser shown in Figures 1 and 2.

Figure 4 is a view of the condenser in side elevation.

Figure 5 is a detail view in top plan of the rotary sheet metal plate which constitutes an adjustable plate or electrode of the condenser;

Figure 6 is a detail view in top plan of the combined presser plate and adjusting finger and showing the same as shaped prior to assembly and to the final bending operation to which it is subjected; and

Figure 7 is a view in end elevation of the structure shown in Figure 6.

Referring to the drawing it will be seen that a trimmer condenser constructed in accordance with the present invention comprises an oblong, plate-like body I of insulating material, which may be constituted of molded and fired ceramic material of high dielectric constant, or of other suitable insulating material. The material of which the dielectric body I of the condenser is formed may be of various suitable compositions.

Preferably, although not necessarily, it is composed of titanium dioxide and a rare earth. For example, it may be any one of the compositions disclosed in the application of George M. Ehlers and R. R. Roup, filed August 25, 1938, Ser. No. 226,734, for Electric capacitors and dielectric for same, assigned to the assignee of this application.

The plate-like body I is formed on its under side with a circular recess 2. This recess is disposed towards one end of the under side of the plate-like body, but is symmetrically disposed with respect to the side edges thereof. Leading from diametrically opposite points of the marginal wall of the recess 2 are grooves 3 and 4, these grooves leading out through the peripheral edges of the body at the ends thereof.

A metallic film 5 is applied to a portion of the bottom of the recess 2 and to the bottom or floor of the groove 3. The portion of this metallic film lying within the recess 2 is generally of semicircular form, although notched slightly at the center, as indicated at 5'. The film 5 may be applied to the recess 2 and groove 3 in various ways. It may be painted or sprayed thereon. Usually silver salts are applied and then reduced either chemically or by heat. The silver film may be copper-plated, if desired. The film 5 constitutes one of the plates or electrodes of the condenser. Its electrical connection with an external circuit is facilitated by virtue of the provision of a terminal 6 which has a portion disposed in the groove 3 in contact with the film 5 and a portion projecting beyond one end of the dielectric body I. The terminal 6 is held in good electrical contact with the film 5 and is mechanically secured to the dielectric body I by means of an eyelet or hollow rivet l. The dielectric body I when molded is formed with an opening to accommodate this eyelet and also is formed with openings 8 adapted to accommodate fastenthe adjustable electrode or plate It) comprises a fiat, smooth surfaced piece of electrically conductive sheet metal of substantially semi-circular. form, as shown in detail in Figure 5. In the assembly the plate I0 is disposed flush up against the surface 2' of the dielectric body I. The plate It! is provided with an apertured hub portion II in which the tubular body portion of an eyelet I2 is fitted whereby the plate III is interconnected with the dielectric body I for rotation relative thereto. Obviously, means other than an eyelet or tubular rivet I2 may be employed to rotatively interconnect the plate Ill and dielectric body I, but the use of an eyelet is especially advantageous since it may be made to serve several other useful functions. In the present construction, the eyelet I2 is also employed to fasten a terminal I3 to the dielectric body I and to electrically conmeet the terminal I3 to the condenser plate I 0, the eyelet I2 being, of course, of electric conductive metal. The terminal I3 extends through the groove 4 and across the uncoated portion of the floor of the recess 2. It terminates, however, in spaced relation with respect to the electrode or plate 5 of the condenser. The inner end of the terminal I3 is apertured to receive the lower end portion of the tubular body of the eyelet I2 and the extreme lower end of the eyelet is upset or riveted over the margin of the aperture in the inner end of the terminal I3, as clearly shown in Figures 2 and 3 of the drawing. The outer ends of the terminals 6 and I3 may project beyond the ends of the plate-like body I, as shown in full in Figures 1 to 4, or these terminals may be bent intermediate the ends into right-angle formation, as shown in dotted lines in Figure 2, to adapt them for connection to an external circuit.

The adjustable condenser plate ill is forced firmly against the surface 2 of the insulating body I, and its adjustment is facilitated by means of the provision of a combined presser plate and adjusting finger, designated as a whole at I 8. The presser plate comprises a generally rectangular body portion I9 of resilient or spring sheet metal. Adjacent one end the body portion I 9 is provided with an aperture 2|] through whichv the upper portion of the tubular shank or body of the eyelet I2 extends. The upper end of the eyelet I2 is flanged over the margin of this aperture 20, as clearly shown in Figure 2. The body portion I9 of the presser plate is arched or bowed longitudinally, and in the assembly and under the securing action of the eyelet I2 the presser plate is intensioned or stressed so as to very effectively perform its function of forcing the. condenser plate I0 against the surface 2 of the insulating body I.

Adjacent one end of the body portion I9 of the presser plate integral laterally projecting wings or extensions M are formed. Driving lugs 22 are struck downwardly from these wings, and in the assembly these driving lugs engage with portions of the transverse edge of the adjustable condenser plate II]. An adjusting finger 25 is illtegrally formed with the end of the body portion ID from which the wings or extensions 2i laterall project. The adjusting finger 25 is first formed up in the manner shown in Figures 6 and 7 to facilitate the assembly of the parts and especially the application of the eyelet I2. After the parts have been assembled, and the eyelet flanged, the adjusting finger is bent down to the position shown in Figures 1, 2, and 4. The body of the adjusting finger is formed with a lengthwise slot 26 adapted to receive a screwdriver, or other suitable tool, to facilitate manipulation of the finger and consequent adjustment of the condenser plate I0. The driving connection between the adjusting finger and the condenser plate is exerted through the driving lugs 22. The adjusting finger is as described integral with one end of the body portion I9 of the presser plate and its rigid interconnection therewith is further enhanced by virtue of the provision of the transverse driving slot 21 in the outturned end 29 of the finger through which a driving lug 29 struck up from the body portion I9 of the presser plate extends.

With this construction, by turning the semi circular metal plate In of the condenser more or less of it may be brought into effective capacitative relationship with the metallic film which constitutes the other plate of the condenser. This, of course, varies the capacity of the condenser over a very wide range and through minute or substantial increments, as may be desired. The dielectric or insulating body constituted as it is of molded ceramic material of high dielectric constant not only provides a highly efiicient dielectric, but, being of substantial mechanical strength, also serves as a support for the other elements of the condenser and as a means of attachment to the device with which the condenser is combined.

By providing the dielectric body in the form of a fiat plate, one surface thereof is adapted to have a metallic film applied thereto, and this may be done in such a way that the film is protected. For example, in the construction shown the film is within the confines of a recess. Furthermore, the other surface of the dielectric body may be lapped or ground to provide a flat plane surface with which the adjustable or rotary electrode may have a flush, firm fit. When so related, and when combined with means for pressing the rotary electrode against the fiat, plane surface of the dielectric body, any air film between the plate and the dielectric body is excluded. Hence, the value of the capacity may be controlled with precision, and with all of this provision is made for very simple and practical adjustment of the condenser.

While we have shown and described one construction in which the invention may be advantageously embodied, it is to be understood that the construction shown has been selected merely for the purpose of illustration or example, and that various changes in the size, shape, and arrangement of the parts may be made without departing from the spirit of the invention or the scope of the subjoined claims.

We claim:

1. A trimmer condenser of the character described comprising a fiat plate-like body portion of insulating material, a metallic film applied to one face of the body portion, a condenser plate of sheet metal rotatably mounted on a surface of the body opposed to that with which the fixed plate is applied whereby the angular relationship between the plates may be changed to vary the effective capacity of the condenser, a presser plate connected to said rotary condenser plate for rotation therewith and pressing the rotatable condenser plate firmly against the surface of the body portion with which it is engaged in all angular adjustments thereof, and an adjusting finger integral with said presser plate and overlying the same, said adjusting finger having a slot adapted to cooperate with an adjusting tool.

2. A trimmer condenser of the character described comprising a ceramic plate-like body of insulating material providing the dielectric of the condenser and the support for the parts thereof, said plate-like body having a circular recess on the under side thereof and having grooves leading from said recess out through the peripheral edges of the ends of the body, a substantially semi-circular metallic film applied to the bottom surface of the recess and having an extension applied to the floor of the adjacent groove of the body, a terminal having a portion in electrical contact with the portion of the film located in said groove and secured to the dielectric body, a semi-circular metal plate fiushly engaged with the surface of the body opposite the recess, means pivotally connecting said plate to said body, a terminal having a portion in said recess but spaced from the metallic film, said terminal having a portion extending out through one of said grooves and projecting from the body, said terminal being electrically connected with said metallic plate, means for rotating said metallic plate, and means for pressing said metallic plate firmly against the body of the dielectric.

3. A trimmer condenser comprising a fiat, single plate-like body constituted of ceramic material, said body having one face fiat and plane and having its opposite face provided with a circular recess and with alined-grooves extending from diametrically opposite points of the recess out through the peripheral edges at the ends of the body, an electrode in the form of a film deposited on approximately one-half of the surface of said recess and on the surface of the adjacent groove, a terminal in electrical contact with the portion of the film located in said groove, said terminal being secured to said body and projecting therebeyond, a rotary electrode in the form of a semi-circular plate positioned flatly against the plane surface of said body, an eyelet connecting said rotary electrode to said body for rotation, and a second terminal connected to said eyelet and projecting out through said other groove.

4. A trimmer condenser of the character described comprising a fiat plate-like body portion of insulating material, a metallic film applied to one face of the body portion, a metallic condenser plate rotatably mounted on a surface of the body opposed to that on which the fixed plate is applied whereby the angular relationship between the plates may be changed to vary the effective capacity of the condenser, a presser plate connected to said rotary condenser plate for rotation therewith and pressing the rotatable condenser plate firmly against the surface of the body portion with which it is engaged in all angular adjustments thereof, an adjusting finger integral with said presser plate and overlying the same, and a tongue and slot connection between the outer end of the adjusting finger and the presser plate.

5. A trimmer condenser comprising a flat platelike body of insulating'material, a metallic film applied to one face of the body, a metallic condenser plate fitted flush against the other face of the body, an eyelet connecting said metallic condenser plate to said body for rotation, a presser plate connected to said metallic condenser plate for rotation therewith and pressing the same firmly against the surface of the body with which it is engaged in all angular adjustments thereof, and an adjusting finger integral with said presser plate and overlying the same and said eyelet, said presser plate and said adjusting finger being constituted of sheet metal sufficiently resilient to enable them to be bent into its final shape and sufiiciently stiff to maintain their final set and shape in the assembly.

GEORGE M. EHLE'RS. JOHN S. COLDWELL. GEORGE KODAMA. 

